Although the internet page return a ok respond, this page takes a long time to load

I'm writing an application that tests the login screen of a web site with a chromium web browser in c#. Naturally I manage my processes by filling in certain fields from website tags like ids, names etc. But we have some websites that is still loading even though the page return a positive response. In the meantime the program can not find these tags on this page. Therefore the program can not find these tags, ids or names on this page. How can i fix this? I find a solution with thread sleeping. But its not effective solution for me. Please say another solution..